1. Field of the Invention:
The present invention relates to a liquid crystal display (hereinafter, referred to LCD) device, and more particularly to a structural improvement of the same device.
2. Description of the Related Art:
In recent years, LCD devices using liquid crystal such as twisted nematic (TN) liquid crystal have been developed to an extent of commercial use in some industrial fields including wrist watches, disk-top calculators and so on. For TV display devices, word-processors and other information display devices, active-matrix type LCD devices attract many attentions. Those active-matrix type LCD devices are composed of a first board having a plane electrode held at a reference potential, a second board of transparent material on which there provides a lattice of conductive stripes and a pair of thin film transistor (TFT) and picture element electrode at each crossing point of the conductive stripes, and a liquid crystal interposed between the first and second boards. The TFT's are insulated gate field effect transistors having polycrystalline silicone or amorphous silicon at a channel portion between source and drain regions.
For improving the quality of produced picture on the active-matrix type LCD devices, it is necessary to increase the density of picture elements, causing an increment of the conductive stripes to be scanned. The scanning signals are produced with semiconductor integrated circuit (IC) which is formed in a monocrystalline silicon substrate. The IC is difficult to be formed with use of the polycrystalline or amorphous silicon, due to their crystal imperfection.
The LCD device and the IC for driving the LCD are separately formed and wired therebetween. However, in the LCD device having picture elements of 400.times.600, there are 400 conductive stripes in a vertical direction and 640 conductive stripes in a horizontal direction. Thus, 1,040 interconnections are required in one display apparatus.
Although the interconnections are formed by wire-bonding process, the 1,040 or more interconnections increase a probability of connection errors and rise a production cost. Technically, such large number of interconnections on a small area is an upper limit of present connection technique.
The LCD device in which an LCD panel and a driving circuit are integrated on a single board has been proposed on pages 48 to 49 of "Society for Information Display, International Symposium, Digest of Technical Papers, 82" (referred to "SID 82 DIGEST") and on pages 316 to 319 of "Society for Information Display, International Symposium, Digest of Technical papers, 84" (referred to "SID 84 DIGEST"). The SID 82 DIGEST formed both of LCD panel and driving circuit on a monocrystalline silicon substrate. The monocrystalline silicon substrate is not a transparent material. The proposed LCD device is not used as a light transmission type device. Even in a case using as a light reflection type device, the produced picture has a poor contrast. The SID 84 DIGEST formed both of them on a glass substrate using polycrystalline silicon. The driving circuit is formed of TFT's using polycrystalline silicon and has a limited low operating frequency. The reproduced picture is not stable. The reproduced picture quality is insufficient for commercial use. Furthermore, it is difficult to form the driving circuit into a small area to miniaturize the LCD device.